Add spin_loop_hint intrinsic

src/libcore/hint.rs

@@ -62,13 +62,6 @@ pub unsafe fn unreachable_unchecked() -> ! {
 #[inline]
 #[unstable(feature = "renamed_spin_loop", issue = "55002")]
 pub fn spin_loop() {
-    #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
-    unsafe {
-        asm!("pause" ::: "memory" : "volatile");
-    }
-
-    #[cfg(target_arch = "aarch64")]
-    unsafe {
-        asm!("yield" ::: "memory" : "volatile");
-    }
+    #[cfg(not(stage0))]
+    intrinsics::spin_loop_hint();
 }

src/libcore/intrinsics.rs

@@ -1308,6 +1308,9 @@ extern "rust-intrinsic" {
     /// Emits a `!nontemporal` store according to LLVM (see their docs).
     /// Probably will never become stable.
     pub fn nontemporal_store<T>(ptr: *mut T, val: T);
+
+    #[cfg(not(stage0))]
+    pub fn spin_loop_hint();
 }
 
 mod real_intrinsics {

src/librustc_codegen_llvm/intrinsic.rs

@@ -19,7 +19,7 @@ use rustc::ty::{self, Ty};
 use rustc::ty::layout::{self, LayoutOf, HasTyCtxt, Primitive};
 use rustc_codegen_ssa::common::{IntPredicate, TypeKind};
 use rustc::hir;
-use syntax::ast::{self, FloatTy};
+use syntax::ast::{self, FloatTy, AsmDialect};
 use syntax::symbol::Symbol;
 
 use rustc_codegen_ssa::traits::*;
@@ -28,6 +28,7 @@ use rustc::session::Session;
 use syntax_pos::Span;
 
 use std::cmp::Ordering;
+use std::ffi::CStr;
 use std::{iter, i128, u128};
 
 fn get_simple_intrinsic(cx: &CodegenCx<'ll, '_>, name: &str) -> Option<&'ll Value> {
@@ -689,6 +690,27 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
                 return;
             }
 
+            "spin_loop_hint" => {
+                let asm = match &*self.tcx().sess.target.target.arch {
+                    "x86" | "x86_64" => b"pause\0",
+                    "aarch64" => b"yield\0",
+                    _ => return,
+                };
+                let r = self.inline_asm_call(
+                    CStr::from_bytes_with_nul(asm).unwrap(),
+                    CStr::from_bytes_with_nul(b"r,~{memory}\0").unwrap(),
+                    &[],
+                    self.type_void(),
+                    true,
+                    false,
+                    AsmDialect::Att,
+                );
+                if r.is_none() {
+                    bug!("broken spin_loop_hint");
+                }
+                return;
+            }
+
             _ => bug!("unknown intrinsic '{}'", name),
         };
 

src/librustc_typeck/check/intrinsic.rs

@@ -70,7 +70,8 @@ pub fn intrisic_operation_unsafety(intrinsic: &str) -> hir::Unsafety {
         "overflowing_add" | "overflowing_sub" | "overflowing_mul" |
         "saturating_add" | "saturating_sub" |
         "rotate_left" | "rotate_right" |
-        "ctpop" | "ctlz" | "cttz" | "bswap" | "bitreverse"
+        "ctpop" | "ctlz" | "cttz" | "bswap" | "bitreverse" |
+        "spin_loop_hint"
         => hir::Unsafety::Normal,
         _ => hir::Unsafety::Unsafe,
     }
@@ -379,6 +380,8 @@ pub fn check_intrinsic_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                 (1, vec![ tcx.mk_mut_ptr(param(0)), param(0) ], tcx.mk_unit())
             }
 
+            "spin_loop_hint" => (0, vec![], tcx.mk_unit()),
+
             ref other => {
                 struct_span_err!(tcx.sess, it.span, E0093,
                                  "unrecognized intrinsic function: `{}`",